The present invention relates to a throttle valve opened amount calculator.
Automobiles are provided with throttle valve sensors. A throttle valve opened amount sensor detects the opened amount of a throttle valve, which is arranged in an intake passage and opened and closed in accordance with the depressed amount of an acceleration pedal. The opened amount of the throttle valve is used as a parameter to perform engine control, such as fuel injection and ignition adjustment. In a four wheel drive vehicle, the throttle valve opened amount is used as a parameter for controlling distribution of the drive force of a transmission installed in the vehicle.
The throttle valve opened amount xcex8 is calculated as described below.
A CPU receives a detection signal (detection voltage TPV) from a throttle valve sensor and uses the detection voltage TPV and predetermined data to obtain the throttle valve opened amount xcex8. More specifically, the CPU subtracts a predetermined reference value (zero point detection value TPV0) from the detection voltage TPV to obtain an absolute value (TPA=TPV-TPV0).
The CPU uses map data of the throttle valve opened amount xcex8 corresponding to the absolute value TPA to obtain the throttle valve opened amount xcex8 corresponding to the present detection voltage (absolute value TPA). The zero point detection value TPV0 is the voltage value output from the throttle valve sensor when the throttle valve is fully closed (xcex8=0).
The throttle valve opened amount xcex8 is obtained from the absolute value TPA for the following reason. There are differences between throttle valve sensors, which are installed in automobiles. Thus, the zero point detection value TPV0 differs between sensors (e.g., 0.6xc2x10.2V). Accordingly, the zero point detection value TPV0 is obtained for each throttle valve sensor and the absolute value TPA is obtained from the zero point detection value TPV0. By obtaining the zero point detection value TPV0 in accordance with the absolute value TPA, errors that result from differences between sensors are prevented and the throttle valve opened amount xcex8 is accurately obtained. In this state, the same map data for obtaining the throttle valve opened amount xcex8 is used for every automobile even though there may be differences between throttle valve sensors.
Changes in the sensor caused by reasons such as wear occur as time passes by. Thus, the CPU periodically corrects the zero point detection value TPV0. When the detection value TPV is smaller than the zero point detection value TPV0, the CPU sets the detection voltage TPV as a new zero point detection value TPV. The CPU obtains the throttle valve opened amount xcex8 in accordance with the updated zero point detection value TPV0. Accordingly, the zero point detection value TPV0 is replaced by a smaller value whenever the detection voltage TPV is less than the zero point detection value TPV0.
In the prior art process for correcting the zero point detection value TPV0, when the detection voltage TPV is less than the present zero point detection value TPV0, the zero point detection value TPV0 is immediately updated with the detection voltage TPV. Thus, when the power supply voltage supplied to the sensor decreases for one reason or another or when the detection voltage TPV momentarily decreases due to noise, there is a possibility that the CPU may set the detection voltage TPV as the new zero point detection value TPV0.
The drive force transmission of a four wheel drive vehicle is normally separated from the throttle valve sensor, which is controlled by an engine controller. Thus, the signal line of the sensor is long and is apt to being affected by noise. Consequently, the zero point detection value TPV0 may be updated when not necessary.
It is an object of the present invention to provide a throttle valve opened amount calculator that accurately calculates the throttle valve opened amount regardless of voltage fluctuation or noise.
To achieve the above object, the present invention provides a throttle valve opened amount calculator. The calculator includes a valve sensor for detecting an opened amount of a throttle valve to generate a detection voltage. A memory is connected to the valve sensor to store an initial zero point detection value. The initial zero point detection value is the detection voltage output from the throttle valve sensor when the throttle valve is fully closed. A calculation circuit is connected to the valve sensor and the memory to obtain the difference between the detection voltage and the initial zero point detection value and to calculate the opened amount of the throttle valve with the difference. When a plurality of detection voltages that are less than the initial zero point detection value are generated, the calculation circuit calculates a new zero point detection value that is greater than a smallest one of the plurality of detection voltages by a predetermined value and updates the initial zero point detection value with the new zero point detection value.
A further perspective of the present invention is a method for calculating an opened amount of a throttle valve. The method includes detecting the opened amount of the throttle valve to generate a detection voltage, storing an initial zero point detection value in a memory, and calculating the opened amount of the throttle valve from a difference between the detection voltage and the initial zero point detection value. The initial zero point detection value is the detection voltage when the throttle valve is fully closed. When a plurality of detection voltages that are less than the initial zero point detection value are generated, a new zero point detection value that is greater than a smallest one of the plurality of detection voltages by a predetermined value is calculated. The initial zero point detection value is updated with the new zero point detection value.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.